1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus adapted to make a diagnostic examination by transmitting an ultrasonic wave to a subject and collecting corresponding components echoed back from the subject.
2. Description of the Related Art
The ultrasonic diagnostic apparatus includes an ultrasonic probe which is adapted to transmit an ultra sonic wave toward a subject upon application of a drive pulse (also referred to an excitation pulse) and receive corresponding components echoed back from the subject.
In the diagnostic examination of the subject, different types of ultrasonic probes are prepared for the ultrasonic diagnostic apparatus and are properly and selectively utilized according to which part of the subject is to be examined and to the purpose for which the probe is used.
The ultrasonic diagnostic apparatus is equipped with an ultrasonic probe having an array of ultrasonic oscillation elements for electronic scan, such as a linear scan and sector scan, to be conducted, and includes a transmit/receive circuit having a plurality of transmit channels for allowing a drive pulse to be applied to a corresponding ultrasonic oscillation element and a plurality of receive channels for echo signal processing. The transmit/receive circuit is for an electronic scan type ultrasonic probe only and the input/output impedance etc. are set to an optimal value for the ultrasonic oscillation element of the probe.
There is sometimes the case where it is desired to collect the ultrasonic wave information from a subject with the use of, for example, a mechanical scan type ultrasonic probe in distinct from an electronic scan type ultrasonic probe. The ultrasonic probe for mechanical scan includes, for example, an annular array type composed of a concentric array of ring like ultrasonic oscillation elements for allowing the use of electronic focusing and a single type composed of a single circular ultrasonic oscillation element. Any of these types of probes is greater in the area of the oscillation element, but smaller in the impedance, than the ultrasonic probe for electronic scan. As set out above, the transmit/receive circuit is optimally designed with respect to the ultrasonic probe for electronic scan and, even if the mechanically scan type ultrasonic probe is driven with the transmit/receive circuit operated without being modified, the load (ultrasonic oscillation element) drive capability and S/N ratio at the receive system are lowered, making it difficult to collect the ultrasonic wave information of the subject in a high S/N ratio. It is necessary, at any rate, to provide an extra transmit/receive circuit for the mechanical scan type ultrasonic probe only. However, if such a type is so provided, then the resultant apparatus becomes large in size and high in cost.